A physical quantity sensor having a sensor chip disposed on a circuit chip is, for example, disclosed in U.S. Pat. No. 6,151,966. The sensor chip is laminated on the circuit chip through an adhesive layer. The sensor chip includes a movable electrode and a fixed electrode, which are supported with a substrate.
The movable electrode is movable in a direction parallel to the substrate. The movable electrode faces the fixed electrode so that a detection distance therebetween is formed. When a physical quantity is applied to the sensor, the movable electrode is displaced so that the detection distance is changed. The change of the detection distance is measured by an electric circuit so that the physical quantity is detected.
In the above physical quantity sensor, it is required to detect a displacement error of the movable electrode. Therefore, an additional construction is necessitated to detect the displacement error. For example, the substrate extends in a horizontal direction of the substrate to form a surface electrode for applying an electric potential between the substrate and the movable electrode. This electric potential generated between the substrate and the movable electrode provides an electro static force therebetween so that the displacement error is detected. Accordingly, the dimensions of the sensor chip become larger. Further, it is required that the surface electrode is connected to the circuit chip with a bonding wire. Thus, the dimensions of the physical quantity sensor become larger, and the manufacturing process of the sensor becomes complicated.